In heavy equipment and other machinery having an engine, torque converter, transmission, driveline, axles and an earth moving implement, it is important to match the power output of the engine with the torque capability of the powertrain components. For example, if the engine produces power above the rating of the powertrain components, then the powertrain components may deteriorate and fail sooner than expected. However, selecting powertrain components with a power rating that exceeds the power output of the engine and torque converter increases the cost of the powertrain components. Thus, it is advantageous to match the power output of the engine and torque converter closely to the torque ratings of the powertrain components.
As is known in the art, the maximum torque output of the torque converter varies with engine speed and with output speed of the torque converter. The torque produced within the transmission and other powertrain components is a function of the engine speed, torque converter output speed and transmission gear ratio. Ideally, the transmission should be selected so that its components can accept the maximum torque output of the torque converter. However, the maximum torque output may occur over a narrow band of engine output speeds or in a specific gear ratio. At other speeds or in other gear ratios, the torque on the transmission components may be less. For those speeds and gear ratios it would be possible to select less expensive components. Thus, for some applications, it may be preferable to limit the amount of power the engine can produce during certain gear selections and speeds in order to reduce the maximum torque on the transmission and powertrain components. This, in turn, will permit the use of less expensive transmission components.
Prior art controllers are known which limit the engine power output based on gear selection of the transmission. Such controllers may perform satisfactorily on vehicles and other equipment without other systems requiring engine power. For example, on wheel loaders and other equipment with earth moving implements, the implement is typically powered by a hydraulic system that is powered by the engine. In those cases, the power produced by the engine may be demanded by the hydraulic system and not the transmission. Thus, there may be instances when full engine power might damage the transmission components if all of the power is applied to the transmission. However, if the engine power is, at least in part, being diverted to the hydraulic system, then full engine power might be appropriate. Prior art controllers that limit engine power, do not consider hydraulic system power requirements.
One solution might be to include a pressure transducer or other device to sense the power demands of the hydraulic system. However, those sensors are expensive. It would be preferable to have a system that can account for hydraulic system demand using sensors already present on the vehicle and reduce engine power when excessive torque levels might result.